The present invention is directed to the sensing arts and more particularly to a grain sensor of the type including a piezoelectric element which produces a detectable electrical signal in response to forces imparted thereto. While features of the invention may be adapted to different uses, the disclosure will be directed to a grain sensor of the type utilized to detect grain loss in harvesting machinery.
In harvesting machinery such as a combine, it is desirable to monitor the grain loss during the harvesting operation. In this regard, it is the practice to monitor the quantity of grain discharged in the chaff from the combine machine in order to ensure efficiency of the harvesting operation.
Accordingly, sensors and cooperating monitoring systems have heretofore been developed for the foregoing purpose. In such systems the sensing elements or sensors are customarily located generally adjacent the points of the combine machine where waste or chaff material exits, in order to attempt to monitor the amount of grain carried off with this waste material. Consequently, the discharge ends of the walker, sieve and/or shoe portions of the combine have therefore often been provided with suitable grain loss sensors.
Generally speaking, the grain loss sensors heretofore used have included a piezoelectric element mounted to an elongate, generally flat, rigid board, generally referred to as a sounding board. Hence waste mateiral including grain particles discharged from the shoe, sieve and/or walker assembled of the combine machine impinges upon the sounding board. The sounding board in turn transmits the vibrational or other forces generated by such impingement to a piezoelectric element, which is usually affixed to the back sides thereof.
In the field, some problems have been experienced with the foregoing type of sensor structure. Namely, the sounding board, which is constantly subjected to bombardment by materials discharged form the combine, often becomes damaged or broken after a relatively short period of use. Initially, a solution to this problem was attempted by utilizing more durable materials in the manufacture of the sounding board. Additionally, it was found tht the piezoelectric element was often activated by vibration in the machinery, rather than by discharge material impinging on the sounding board. To correct this problem rubber bushings were added to the mountings for the sensors, and in some cases a comb assembly was added over the sounding board to allow lighter waste material to pass over the top of the sounding board.
Even with the foregoing modifications, both the relatively delicate piezoelectric elements and the sounding boards were often subject to environmental abuse and durability problems which reduced their expected service life. In this regard, even when constructed from a more durable material, the sounding board remained particularly susceptible to damage and breakage at its edges.
Moreover, each of the foregoing modifications resulted in the addition of parts, and hence labor in the construction of the sensor assemblies, with attendant cost escalation.